The spread of wireless communications apparatus such as portable telephone and PHS is remarkable. Wireless communications apparatus for use in wireless data communications network called wireless LAN have rapidly spread in offices, stores, factories, warehouses, etc. A technique is known for executing an electric radiation barrier material made of metal foil or mesh or electrically-conductive fiber for the purpose of preventing the entrance of noise electric radiation from the exterior of a specific room such as office or the leakage of data to the exterior of the room in the case where these wireless communications apparatus are used in the specific room.
However, when such an electric radiation barrier material is applied, the interior of the room exhibits a high reflectivity of electric radiation, causing electric radiation transmitted from wireless communications apparatus to be reflected by the inner wall, ceiling, floor, steel furniture and building material, etc. Thus, reflected electric radiations having different phases reach the receiving terminal. Further, multiple reflected electric radiations from the ceiling, wall and floor reach the receiving terminal, making it impossible for received electric radiation to be recognized as a normal signal. Accordingly, the wireless communications require an abnormally prolonged time or are disabled. Even when the foregoing electric radiation material is not intentionally applied, the modern offices often comprise a metallic deck plate provided on the ceiling and floor or a metallic double-floor panel provided on the floor, giving an atmosphere causing vertical reflection of electric radiation. These offices often comprise a steel partition wall as a wall, giving an atmosphere causing horizontal reflection of electric radiation.
When wireless communications apparatus are used in these interior atmospheres, maltransmission due to reflected electric radiations having difference phases or obstruction in communications due to the effect of reflected electric radiations which have arrived with a time lag can occur as in the case where the foregoing electric radiation barrier material is intentionally applied. In order to countermeasure against these phenomena, it is useful to apply a member for inhibiting the reflection of electric radiation to the interior material of the room. A ferrite tile or a cement material or plasterboard having ferrite or an electrically-conductive material incorporated therein has heretofore been used. Further, an execution method has been proposed involving the integration of a felt-like electric radiation-absorbing material with the back surface or the base board of the ceiling or floor.
However, the foregoing conventional execution method is troublesome. In addition, the foregoing execution method is disadvantageous in that the ferrite tile or a cement material or plasterboard having ferrite or an electrically-conductive material incorporated therein has a high specific gravity and thus takes much time to apply. These materials are also expensive. Supposing that the prevention of reflection of electric radiation is carried out by applying an electric radiation-absorbing material to the floor or wall among various positions in the interior materials, it is usual that steel desks are installed on the floor, eventually causing the floor to act as an electric radiation reflecting material that can impair the electric radiation-absorbing effect of the electric radiation-absorbing material applied to the floor. Even when an electric radiation-absorbing material is applied to the wall of the room, steel bookshelves or rockers are often installed in front of the wall, eventually causing the most part of the wall to act as an electric radiation reflecting material that can impair the effect of the electric radiation-absorbing material thus applied.
On the contrary, when an electric radiation-absorbing material is applied to the ceiling, there is no case where some electric radiation reflecting materials are applied to the interior side of the ceiling. Thus, even when steel desks or bookshelves are installed in the room to change the conditions of the interior of the room, the electric radiation-absorbing properties of the ceiling can be rarely impaired. Further, since the transmission-reception apparatus of wireless LAN are often installed on desks or personal computers on the desks during use, electric radiations thus transmitted are often reflected by the ceiling. Thus, in order to lessen reflected electric radiations, it is preferred that an electric radiation-absorbing material be installed on the ceiling.
However, the foregoing conventional execution method is disadvantageous in that the ferrite tile or ferrite-containing plasterboard used not only can be hardly applied due to its high specific gravity but also is expensive. This method is further disadvantageous in that the plasterboard becomes black. These materials are also disadvantageous in earthquake resistance.